The wireless ad hoc network is a technique in which wireless communication apparatuses exchange information on an equal footing without a particular centralized control station to keep communication routes autonomously for forming a network. Routing control in the ad hoc network can be broadly divided into two schemes. One is a distance vector type, and another is a link state type.
In the two schemes, the present invention relates to the distance vector type (non-patent documents 1, 2 and 3) represented by AODV (Ad hoc On-Demand Distance Vector Routing), DSR (Dynamic Source Routing) or STP (Spanning Tree Protocol).
FIG. 1 shows a routing control scheme in a conventional distance vector type algorithm. In the distance vector type algorithm, a source node advertises a request frame, and a destination node sends a route acknowledgement frame as a response signal of the request frame.
An intermediate node that receives request frames stores each distance (communication cost) described in the request frames so as to transfer only a frame describing the smallest communication cost. By repeating this operation, the destination node can ascertain a route by which communication cost from the source node becomes smallest. The destination node that stores an optimal route sends a route acknowledgement frame along the stored route in the reverse order. The passing route of the route acknowledgement frame becomes the optimum route from the source node to the destination node.
In the ad hoc network, terminals autonomously forms a network. Therefore, when traffic concentrates on a particular terminal, communication delay occurs for all terminals that exchange data via the particular terminal.
As a means for solving this problem, in Japanese Laid-Open Patent Application No. 2000-69046 (Patent document 1), it is proposed to apply a concept of the spanning tree used for wired networks to the wireless network. In addition, a mechanism is proposed for avoiding occurrence of relay loop when constructing a spanning tree in a wireless network so as to avoid useless relay as much as possible (refer to patent documents 2 and 3, for example).
In addition, for avoiding effects due to load concentration to a particular node, it is proposed to perform routing control using load of nodes as an index in an ad hoc network (refer to non-patent documents 4 and 5, for example). Other than those, a method is proposed for switching between link cost that is communication available time between nodes and node cost that is busy ratio of nodes (refer to non-patent document 6, for example).
However, in these techniques, each wireless communication apparatus has a single wireless interface. Therefore, when the wireless communication apparatus has a plurality of wireless interfaces, further improvement is required.
On the other hand, when the wireless communication apparatus has a plurality of wireless interfaces, it is proposed to decrease interference so as to use wireless resources efficiently (refer to patent document 7, for example), but concentration of load to a node is not considered.                [Patent document 1] Japanese Laid-Open Patent Application No. 2000-69046        [Patent document 2] Japanese Laid-Open Patent Application No. 2000-78147        [Patent document 3] Japanese Laid-Open Patent Application No. 2003-188811        [Non-Patent document 1] IETF RFC3561: AODV routing        [Non-Patent document 2] Internet Draft: The Dynamic Source Routing Protocol        [Non-Patent document 3] IEEE802.1D std. Spanning Tree Protocol        [Non-Patent document 4] Dynamic Load-Aware Routing in Ad hoc Network, Proc. ICC 2001, June, 2001        [Non-Patent document 5] Performance evaluation for mobile ad hoc routing protocols based on link expiration time and load of node, IEICE TRANSACTIONS, Vol. 85-B, No. 12, 2002        [Non-Patent document 6] Metric selection mobile ad hoc routing protocol based on link and node costs, IEICE Technical Report, NS2003-80, 2003        [Non-Patent document 7] A Multi-Radio Unification Protocol for IEEE802.11 Wireless Networks, Microsoft, 2003        